On the Wall Street Journal web site, Prof. Anthony Gill gives a succinct and fascinating view of why the Taliban in Afghanistan have been so rapidly successful in taking territory, recently and decades ago.
What might seem counter-intuitive to a lot of people, strict religious organizations are really vibrant communities and do not drive everyone away with their rules, instead "...Strict behavioral codes (e.g., no drinking, refuse blood transfusions) and stigmatizing behavior (e.g., wear distinctive clothes) weed out free riders in groups and enhance cooperation. Religious denominations are essentially club goods wherein members share in many collective benefits (e.g., welfare provision, fellowship)...If everyone chips in, the organization is vibrant. However, if many members are there just to receive those benefits but do not participate (i.e. free riders), the quality of the good is dissipated and the organization becomes anemic."
The Taliban could also provide stability, "Following the defeat of the Soviet occupation in 1989...Afghanistan fell into a disorganized mess of rival ethnic clans vying for political and economic power. A disunified governing system could not effectively collect taxes and the nation’s infrastructure, including the ability to guarantee basic market interactions, fell into total disrepair, making it one of the world’s most impoverished nations.
The Taliban, however, proved to be the only unifying entity that could guarantee safe trade routes, collect taxes without excessively plundering the population, and provide essential public goods to key cities."